The present invention relates to improved strain-gage transducers having relatively small bulk and exhibiting advantageously linear performance characteristics, due principally to unique load-transmitting interconnections between their load-receiving and load-supporting parts, and, in one particular aspect, to readily-gaged downsized coaxial-type load cells wherein linearity and precision are promoted by mechanically coupling concentric inner and outer structural elements via several relatively elongated shear-sensing beams disposed along angularly-spaced chords of an annular region between those elements, and by providing rugged integral end connections for the beams which extend inwardly and outwardly at angular positions between the beams.
Transducers in which strain gages respond to and electrically characterize elastic deformations of members experiencing loading have long been known in a variety of forms and sizes, for purposes of characterizing such phenomena as force, torque, weight and pressure. To promote convenience of usage in the trade by customers, some such transducers are fashioned as sealed cells which may be bodily introduced into operating environments where they will function as part of a load-carrying structure at the same time that they perform needed measurements; tanks, bins, rolling-mill equipment and the like commonly incorporate such cells, and it is routinely required that they occupy as little space as possible while nevertheless being capable of withstanding very high peak loads and of performing precision measurements within ranges of special interest.
One form of cell which has earned a deservedly outstanding reputation in satisfying such rigorous requirements has been of a generally concentric or coaxial configuration involving a central load-receiving portion and an outer ring-like portion, the two being connected together at several equally-spaced angular positions by integral short radial "spokes". Such radial interconnections have been conveniently formed by material left in place between adjacent drilled holes, and load-related shear strains developed in those radially-extending interconnections have been characterized electrically with the aid of strain gages bonded at appropriate sites (U.S. Pat. Nos. 3,037,178 and 3,958,456). Unfortunately, those surfaces along which shear strain would best be sensed by the gages have curvatures of the drilled holes, and their most critical orientations are along the thinnest portions between adjacent curved surfaces and lie within the holes. Installation of the gages tends to be highly exacting and troublesome, especially when the hole sizes are small. Although it is generally desirable to minimize the overall heights and diameters of such cells, for given capacities, reductions in size tend to be at the expense of impaired performance because of adverse influences of twisting or other mechanical distortions of less rigid central and outer portions and because of "end effects" associated with weaker end connections for the radial spokes. In the latter connection, there is of course less room for sturdy end connections of the radial spokes as the cell diameter is reduced, and the short radial beams can then witness strains which are in varying rather than fixed patterns; such variations in turn affect the strain-gage outputs and tend to cause cell outputs with loading to be at least non-linear, if not inaccurate.
In accordance with improvements taught here, the placements of gages in coxial load cells and the like is rendered less critical, and ample access for their convenient installation is provided, even though overall cell size is reduced. Moreover, the strain-sensitive beam elements which interconnect inner and outer load-transmitting portions in such devices are flat-sided and elongated and are not oriented radially, and relatively massive end connections which do not deform readily are advantageously accommodated in spaces between the beam elements.